Canada France Hawaii Telescope

New clues about the early evolution of the Solar System revealed with simultaneous observations on Maunakea.

Simultaneous observing on Maunakea. Both telescope are pointing at the same object at the same time. Coordinating observations like this between two major observatories is quite a challenge but provides big returns. Credit: Gemini Observatory/AURA, photo by Joy Pollard.

An international team of astronomers led by Wes Fraser of Queen's University in Belfast used CFHT and Gemini simultaneously to discover a new type of Kuiper Belt Object (KBO) called "Blue Binaries". The wide separation and color of these cold classical Kuiper Belt objects are providing important clues on the early evolution of the solar system. Their findings are published in the April 4 edition of Nature Astronomy.

The Kuiper Belt is a circumstellar disk in the outer Solar System extending from beyond the orbit of Neptune to about 50 AU from the Sun. The dynamical structure of the classical Kuiper Belt is divided in two components. The hot component is made of objects with eccentric and highly inclined orbits. They have a broad range of colors and about 10% of them are binaries. On the other hand, the cold component consist of objects with nearly circular orbits and low inclination. Their colors are typically red and have a higher occurrence of binaries, about 30%.

In February 2013, CFHT started the Outer Solar System Origins Survey (OSSOS), a Large Program that was awarded 560 hours of observing time over 4 years to find and track objects in the outer Solar System using Megaprime. OSSOS was completed in January 2017 and was highly successful, discovering nearly 1000 Trans Neptunian Objects that inhabit the outer Solar system.

The Colors of OSSOS (Col-OSSOS) program aimed to measure the colors of the cold classical Kuiper belt objects found by the OSSOS program. The team used CFHT and Gemini to gather colors from the ultraviolet to the infrared. The need for simultaneous observations came from the fact that these bodies rotate reasonably fast, on the order of one to a few hours so sychronous observations are important to ensure the team observed the same position at the same time in different colors. “Facilitating the simultaneous observations with the Col-OSSOS team and Gemini Observatory was challenging, but paved the way for a greater understanding of the origins of these blue binaries. In tandem, the two facilities observed all the colors of the outer solar system for the Col-OSSOS team” said Todd Burdullis, queued service observing operations specialist at CFHT who was in charge the CFHT observations and a coauthor of the study. Dr. Meg Schwamb, an astronomer at the Gemini Observatory and also a coauthor on the paper added: “Like synchronized swimmers, Gemini North and the Canada-France-Hawaii telescopes coordinated their movements to observe the Col-OSSOS Kuiper belt objects at nearly the same time. This created a unique dataset that the planetesimals’ brightness changes as they rotate, and led to this discovery.”

Five of the OSSOS objects are blue, very peculiar for objects belonging to the cold classical Kuiper Belt which are usually red. Additionally, these blue objects are wide binaries. The presence of so many widely separated blue binaries in the cold classical Kuiper Belt is difficult to explain.

In their Nature paper, the team explored different mechanism that would lead to this configuration and estimated that the best model reproducing the observations is a "push out" by the early phases of the outward migration of Neptune. In order keep the binary systems intact i.e. not splitting them apart, the outward motion of Neptune had to be very smooth and eventless. “This research has opened the window to new aspects of understanding the early stages of planet growth. We now have a solid handle on how and where these blue binaries originated" said Wes Fraser, first author of the study.